1. Field of the Invention
This invention relates to modules and methods for making same.
2. Background Art
Micromechanical (xcexcmechanical) resonators and bandpass filters with frequencies in the low-UHF range (e.g., 35-300 MHz) have recently been demonstrated with performances that rival (and even better in some cases) those of bulky, off-chip crystal and SAW filters used in present-day wireless transceivers. By integrating these xcexcmechanical devices together with transistor circuits using a merged MEMS/transistor process technology, single-chip RF MEMS front-ends using high performance super-heterodyne architectures may eventually become possible. The degree to which MEMS and transistor devices can be modularly combined is of utmost importance for RF MEMS applications, since the performance (e.g., Q, stability) of resonator devices is especially sensitive to fabrication conditions (e.g., temperatures, materials), which are often compromised in insufficiently modular merging processes.
Multichip Module (MCM) technology allows integrated circuits and passive devices to be mounted together on a common interconnecting substrate. Flip-chip solder-bump is a chip attachment technique in which pads and the surface of the chip have solder balls placed on them. The chips are then flipped and mated with an MCM or a PCB, and the soldered reflowed to create a solder joint. This technology has demonstrated promising results for high performance, high frequency MCM-based microprocessors. In MCMs, separate chip modules are flip-chip bonded to a larger substrate to form a complete system, where interconnects and signal lines between modules are formed directly on the substrate. The modules are bonded to the pads on the substrate using either solder or gold bumps, which are normally deposited via evaporation or electroplating.
U.S. Pat. No. 5,995,688 discloses a micro-opto-electromechanical device formed by a flip-chip bonding method.
U.S. Pat. No. 6,214,644 discloses a flip-chip micromachine package wherein a micromachine chip is mounted as a flip-chip to a substrate.
An object of the present invention is to provide an improved module and method of making same.
In carrying out the above object and other objects of the present invention, a method for making a module is provided. The method includes a) providing a device including a first substrate, a microplatform, at least one microplatform bonding, site on the microplatform, a structure fabricated and supported on the microplatform, and a support structure to suspend the microplatform above the first substrate. The method also includes b) providing a second substrate including at least one circuit bonding site thereon and a circuit. The at least one microplatform bonding site is c) aligned with the at least one circuit bonding site and d) the at least one microplatform bonding site is bonded to the at least one circuit bonding site so that the microplatform is bonded to the second substrate at at least one bond.
The structure may be a micromechanical structure and the circuit may be an electronic circuit.
The device may have a plurality of microplatform bonding sites and the second substrate may have a plurality of circuit bonding sites so that the microplatform is bonded to the second substrate at bonds.
The micromechanical structure may be electrically coupled to the electronic circuit by one or more of the bonds.
The first and second substrates may be forced apart to break the support structure and separate the first substrate from the second substrate.
Bond pads and solder bumps may be formed on the second substrate wherein the bond pads serve as the second plurality of bonding sites.
The micromechanical structure may include at least one micromechanical resonator.
The micromechanical structure may be a micromechanical filter.
The at least one microplatform may be defined by a layer of a wafer.
The microplatform may be defined by a silicon device layer of an SOI wafer.
The support structure may include a plurality of tethers for suspending the microplatform above the first substrate.
The second substrate may be a wafer.
The at least one electronic circuit may be a transistor circuit such as a BiCMOS, CMOS, bipolar, SiGe or GaAs circuit.
The step of bonding may include the step of compression bonding and wherein the bonds are compression bonds.
If the device includes a plurality of microplatforms, steps c) and d) can be repeated with the second substrate or at least one other substrate.
The bonds may be selectively heated in a vacuum to vacuum encapsulate the micromechanical structure. Vacuum encapsulation can also be performed by burying the device under the platform under a layer of sealing material.
Further in carrying out the above object and other objects of the present invention, a module is provided. The module includes a device having a microplatform, at least one microplatform bonding site on the microplatform, and a structure fabricated and supported on the microplatform. The module also includes a second substrate including at least one circuit bonding site thereon and a circuit. The microplatform is coupled to the second substrate at the microplatform and circuit bonding sites such that the microplatform is in opposed and spaced relation to the second substrate.
The micromechanical structure may be vacuum encapsulated within a cavity defined by the microplatform and the second substrate.
Similar to the individual modules in MCMs, the micromechanical resonators are directly fabricated on microplatforms, which are flip-chip bonded to the bumps on the transistor circuit wafers, which are, in turn, connected to circuits via metal lines.
An aspect of the present invention is to provide a method for modularly merging two technologies via a process involving fabricating one technology on a platform suspended by tethers on a carrier substrate, then bonding the platform to a receiving substrate and tearing away the carrier substrate, leaving a bonded platform (on which devices in one technology are mounted) over and interconnected to devices in the other technology on the receiving substrate.